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It's good practice on designs using a decoupling cap on most devices. Giving each part a clean voltage is important. Though checking the datasheets for each part is sometimes useful as they may specify the exact value needed for that device. Though, a .1uF is usually fine.
If the 74HC14 is the only IC in you circuit, than colin55 is probably right. But if you have any other ICs, then you should add a cap across each IC to avoid switching current spikes (which generate voltage spikes) from propagating to the other devices.
Logic circuits generally require at least one capacitor in the range 0.01 to 0.1 uF somewhere relatively near the chips. A conservative designer might place one at every chip. If the 74HC14 is near other properly bypassed chips then it can share one of its capacitors. Often the power supply has capacitors on its output and if the 74HC14 is within a few inches it might share that capacitance.
If the 74HC14 is too distant from all of these other caps, it should have a bypass capacitor.
You certainly can build a 74HC14 circuit with no cap, and it will probably work. My personal preference is to build circuits that always work.
I think what Colin says makes sense, it's a Schmitt trigger IC, therefore it should have good noise rejection and shouldn't need a supply bypass capacitor.
Be that as it may, the input can tolerate slow edges but the output switching is still fast with sharp edges which can induce Vcc spike noise. A bypass cap should still be used as it is the output switching that is of concern.
Irregardless of the hysteresis at the input, the output of the HC14 is like any other logic device and will generate transients as the output switches. These transients will appear at a high impedance point such as that of a non bypassed Vcc pin. It is therefore a good idea and common practice to put in a bypass cap . 74HC14 logic shown below.
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